Renewable energy sources include solar energy, wind power, tidal wave energy and the like. A solar power conversion system may include a plurality of solar panels connected in series or in parallel. The output of the solar panels may generate a variable dc voltage depending on a variety of factors such as time of day, location and sun tracking ability. In order to regulate the output of the solar panels, the output of the solar panels may be coupled to a dc/dc converter so as to achieve a regulated output voltage at the output of the dc/dc converter. In addition, the solar panels may be connected with a backup battery system through a battery charge control apparatus. During the day, the backup battery is charged through the output of the solar panels. When the power utility fails or the solar panels are an off-grid power system, the backup battery provides electricity to the loads coupled to the solar panels.
Since the majority of applications may be designed to run on 120 volts ac power, a solar inverter is employed to convert the variable dc output of the photovoltaic modules to a 120 volts ac power source. In order to attenuate undesirable harmonics, a plurality of magnetic devices may be coupled between the solar inverter and the ac power source.
A magnetic device typically includes a magnetic core formed of suitable magnetic materials such as ferrite, powder iron and/or the like. The magnetic device may further include a conductive winding or a plurality of conductive windings. The windings and the current flowing through the windings may generate a magnetic field, which is also known as magnetic flux. In a normal design, the magnetic core usually has a relatively high permeability in comparison with the surrounding medium (e.g., air). As a result, the magnetic flux is confined with the magnetic core, which forms a closed flux path. The magnetic flux provides a medium for storing, transferring or releasing electromagnetic energy.
Coupled inductors are widely used in the power electronics industry. A coupled inductor may comprise two windings magnetically coupled to each other. The two coupled windings may be wound on a same magnetic core (e.g., a toroid core). The first winding generates a first magnetic force, which drives a first magnetic field or flux. The flux generated by the first winding is confined with the magnetic core, which forms a closed flux path. Likewise, the second winding generates a second magnetic force, which drives a second magnetic field, which is confined with the magnetic core. The magnetic material of the magnetic core of a coupled inductor may be of a magnetic permeability greater than that of a surrounding medium (e.g., air). However, the coupling between two windings of the coupled inductor is not perfect. There may be a leakage path between the winding and the surrounding medium having a lower magnetic permeability.